This invention relates to a plasma beam generating method and its generating apparatus, which can generate and control a plasma beam of high energy.
In general, a plasma beam generating apparatus comprises a chamber for defining a discharge space, a plasma source mounted on the chamber to generate a plasma beam, a first magnetic field generating device for generating a first magnetic field to guide the plasma beam generated by the plasma source into the chamber, and an anode portion located within the chamber to receive the plasma beam. The plasma source is generally implemented by a heated cathode.
With respect to the above-mentioned plasma beam generating apparatus, it is recently required to generate a plasma beam of high energy. In order to fulfill such a requirement, it is preferable that a heavy-current discharge, namely, a large-current discharge is carried out at a low voltage in the plasma source.
In order to carry out the heavy-current discharge as mentioned above, a special plasma source is required. However, when the special plasma source is used, the plasma beam generating apparatus becomes complex in structure and expensive in cost. In addition, when the heavy-current discharge is carried out, a large capacity of a carrier gas (for example, argon gas or helium gas) is required and pumping speed thereof must be high. Also from those standpoints, the plasma beam generating apparatus becomes bulky and complex. Additionally, since an operation is carried out under hard conditions, damage to the cathode is increased.
On the other hand, if the plasma source can carry out the heavy-current discharge, it becomes possible to carry out a heavy-current and heavy-voltage discharge. This means that supply energy can be rapidly increased. In order to increase a discharge voltage, it is considered that an electron gun is used as the plasma source. An example of the electron gun is disclosed in Japanese Unexamined Patent Prepublication No. 72155/1977. When the electron gun is used, however, it is necessary that an exhausting section of carrier gas is formed in a large scale or a plurality of exhausting pumps are prepared. As a result, this brings a disadvantage that a capacity of the carrier gas becomes large in addition that the plasma beam generating apparatus becomes a large scale in structure. Furthermore, there is another disadvantage that a plasma state becomes unstable.